FR3039585A1 - ELECTRIC MOTOR FORCE DETECTION NETWORK - Google Patents

Abstract

The present invention describes systems and methods for evaluating a formation and monitoring a tank that utilize electromotive force measurements. A well monitoring system may include: a power supply that generates an electromagnetic field in an underground formation; and a network of electromotive force sensors for measuring the electromotive force at one or more points along a length of the electromotive force sensor array, the electromotive force sensor array including a guide of the electromotive force an optical wave and an electro-optical transducing layer which overlaps one or more lengths of the optical waveguide.

Description

NETWORK FOR DETECTING THE ELECTROMOTIVE FORCE

CONTEXT

The present invention discloses systems and methods for measuring an electromotive force and, more particularly, methods and systems for evaluating the formation and monitoring of the reservoir that utilize electromotive force measurements.

[0002] A variety of electromagnetic tank monitoring solutions based on optical fiber has been developed for evaluation of the formation and monitoring of the tank. A number of these fiber optic tank monitoring solutions include specialized sensor technology and related applications. For example, methods have been developed for detecting the electric field, the magnetic field and the magnetic induction of the optical fiber based on measurements of the stress of the optical fiber. In these methods, individual electromagnetic sensors can be linked to an optical waveguide and interrogated remotely.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate certain aspects of certain embodiments of the present invention, and should not be used to limit or define the invention.

Figure 1 is a diagram of an example of electromotive force detection system.

Figure 2 is a diagram of an example covered optical waveguide placed in a cable contained in a tube.

Figures 3-5 are diagrams illustrating different examples of arrangements of a covered optical waveguide.

Figure 6 is a diagram of an alternative arrangement for the installation of an optical waveguide covered on a casing.

Figures 7-10 are diagrams illustrating different examples of electromotive force detection system arrangements.

Figure 11 is a graph illustrating a concept of methanogenesis and resistivity of a coal field.

Figure 12 is a diagram illustrating an example of a terrestrial model of a methane reservoir of a coal field.

FIG. 13 is a graph of the resistivity of the coal versus the electromotive force of the model in FIG. 12.

FIG. 14 is a graph of the resistivity of the coal versus the sensitivity for the model of FIG. 12.

DETAILED DESCRIPTION

The present invention discloses systems and methods for measuring electromotive force and, more particularly, methods and systems for reservoir formation evaluation and monitoring that utilize electromotive force measurements. The systems and methods can be used as part of an electromagnetic tank monitoring system, which can be deployed permanently or temporarily on a surface (eg, the sea floor) or at the bottom of the well in single or multiple wells. The systems and methods can be used in combination with electrical and / or electromagnetic sources that can be deployed on a surface (eg, the sea floor) or at the bottom of the well in single or multiple wells.

The systems and methods may use an optical waveguide having one or more lengths covered with an electro-optical transduction layer to become the electromagnetic sensor. An electromagnetic field can be generated in the formation which can then be detected along the length of the isolated optical waveguide. Separate intervals of isolated optical waveguides can be interrogated remotely, which can be interrogated remotely, eg, using Sagnac interferometry. The interrogation can measure the electromotive force at different points along the length of the isolated optical waveguide and not the direct measurement of the electromagnetic field.

A well monitoring system can be described. Without limitation, a well monitoring system will now be described. The well monitoring system may include a power supply that generates an electromagnetic field in an underground formation. The well monitoring system may include an electromotive force sensor array for measuring an electromotive force at one or more points along the length of the electromotive force sensor array. The electromotive force sensor array may include an optical waveguide and an electro-optic transduction layer on one or more lengths of the optical waveguide. The electromotive force sensor array can be installed in a wellbore. The network of electromotive force sensors can be installed on the seafloor. The optical waveguide may be wrapped around a casing installed in a wellbore. The electromotive force sensor array may be placed in an interior of a casing installed in a wellbore. The electromotive force sensor array may be coupled to an exterior of casing installed in a wellbore. The electromotive force sensor array may be placed in an optical fiber cable that includes a bundle of optical waveguides. The electro-optical transducing layer may comprise a material selected from the group consisting of a piezoelectric material, an electrostrictive material, and a combination thereof. The electro-optical transducing layer may comprise an electro-optical transducing material and a polymer. A length of the optical waveguide coated with the electrooptic transduction layer may range from 1 m to 10,000 m. The optical waveguide may be periodically covered with the electro-optical transducing layer to provide spaced apart electro-optical transducing layers which each individually have a length ranging from 1m to 1000m and spacing of 1m. at 1000 m. The optical waveguide is covered with a material between spaced electro-optical transduction layers, wherein the material does not bind to the electrooptic transduction layer. The system may also include a computer system for monitoring the measured electromotive force.

[0016] A well monitoring system can be described. Without limitation, the well monitoring method will now be described. The method may include generating an electromagnetic field in a subterranean formation. The method may also include measuring an electromotive force at one or more points along an array of electromotive force sensors. The electromotive force sensor array may include an optical waveguide and an electrooptical transduction layer on one or more lengths of the optical waveguide. The electromotive force sensor array can be installed in a wellbore. The network of electromotive force sensors can be installed on an ocean floor. The optical waveguide may be wrapped around a casing installed in a wellbore. The electromotive force sensor array may be placed in an interior of a casing installed in a wellbore. The electromotive force sensor array may be coupled to an exterior of casing installed in a wellbore. The electromotive force sensor array may be placed in an optical fiber cable that includes a bundle of optical waveguides. The electro-optical transducing layer may comprise a material selected from the group consisting of a piezoelectric material, an electrostrictive material, and a combination thereof. The electro-optical transducing layer may comprise an electro-optical transduction material and a polymer. A length of the optical waveguide coated with the electrooptic transduction layer may range from 1 m to 10,000 m. The optical waveguide may be periodically covered with the electro-optical transducing layer to provide spaced apart electro-optical transducing layers which each individually have a length ranging from 1m to 1000m and spacing of 1m. at 1000 m. The optical waveguide is covered with a material between spaced electro-optical transduction layers, wherein the material does not bind to the electrooptic transduction layer. The measurement of the electromotive force can include the induction of a stress in the optical guide in response to the electromagnetic field. The method may also include generating electromagnetic signal with a wired tool lowered into the wellbore; detecting the electromagnetic signal with the electromotive force sensor array and determining the electromotive impulse response of the electromotive force sensor array at one or more positions of the wired tool. The method may also include generating an electromagnetic field with a wired tool lowered into the wellbore to energize the optical waveguide; and measuring an acoustic signal generated by the optical waveguide in response to the electromagnetic field using acoustic transducers placed on the wired tool. The method may also include monitoring the measured electromotive force to determine the time intervals of fluid substitutions in the subterranean formation. The method may also include monitoring the measured electromotive force to determine the drying of a coal bed methane tank.

FIG. 1 illustrates an exemplary well monitoring system 100 for use in an underground well. Although not illustrated, a drilling platform can be used to dig and complete a well in a typical manner. The drilling system may include a drill string having measurement capabilities during drilling (MWD) or borehole logging (LWD). The illustrative example of Figure 1 may be used with any of the methods and systems described herein.

As illustrated, a wellbore 102 may extend through the subterranean formation 104. While the wellbore 102 is illustrated as extending vertically vertically into the subterranean formation 104, the principles described herein are also applicable. drilling wells that extend at an angle through the subterranean formation 104, such as horizontal and deviated wellbores. A casing 106 may be placed in the wellbore 102. Cement 108 may surround the casing 106 in the wellbore 102. The well may be adapted to guide a desired fluid (e.g., oil and / or gas ) from the bottom of the wellbore 102 to the surface 110.

The well monitoring system 100 may comprise a power source 112 for the injection of current into the subterranean formation 104 through the casing 106. The supply source 112 may be coupled between the casing 106 and a casing 106. return electrode 114. Since the casing 106 may be an electrically conductive material (eg, carbon steel), it may act as a source electrode for the flow of current to the surrounding subsurface formation 104 the wellbore 102. The tubing 106 may also be formed of other materials, such as fiberglass, e.g., when it is not used to transmit a current from a power source 112. The power source 112 may be coupled to the casing 106 at a variety of suitable locations, e.g., at the wellhead or casing 106 in the wellbore 102. Multiple connections of the power source 112 with the casing 106 may be made if necessary. As illustrated, the return electrode 114 should be located away from the casing 106 and below the surface 110. The magnitude and distribution of the flow of current in the subterranean formation 104 can vary depending on the source of the voltage and the resistivity profile of the formation.

The well monitoring system 100 may also include an optical fiber cable 116. As illustrated, the optical fiber cable 116 may be placed in the wellbore 102. For example, the optical fiber cable 116 may be placed along an outer portion of the casing 106. In addition, the optical fiber cable 116 may be placed in or coupled to an inner portion of the casing 106. Still with reference to FIG. an example of an optical fiber cable 116 with a cut-out portion so that the inside of the optical fiber cable 116 is illustrated. In FIG. 2, the optical fiber cable 116 may comprise an optical waveguide beam 118. The optical waveguides 118 may each be a monomodal or multimodal optical waveguide. Examples of suitable optical waveguides 118 may include optical fibers and / or optical ribbons with a silica or plastic core. The optical waveguides 118 may each be deposited in a polymer pad 120. The polymer pad 120 may be any polymeric pad to protect the interior of the optical waveguides 118 from damage, eg, a buffer polymer made of polyimide or acrylate. As illustrated in FIG. 2, the optical waveguides 118 may be bundled into a jacket 122. The jacket 122 may comprise one or more layers and may also include any suitable material for protecting the waveguides. Examples of such materials may include, without limitation, plastics, metals, etc. In FIG. 2, the jacket 122 may comprise a polymer layer 124 and a metal layer 126. While FIG. 2 illustrates an optical waveguide bundle 118 in the optical fiber cable 116, other configurations of the optical fiber cable 116 may be used, such as, for example, a single optical waveguide 118 placed in the shirt 122.

As illustrated in Figure 2, at least one of the optical waveguides 118 may be at least partially covered by an electro-optical transduction layer 128. When the electro-optical transduction layer 128 is exposed to a time-varying electromagnetic field, e.g., with a component in the direction of the axis of the optical waveguide 118, the electro-optical transducing layer 128 may be deformed, as, e.g. ., expansion or contraction. The mechanical coupling of the electro-optical transducing layer 128 to the optical waveguide 118 must ensure that deformation of the electro-optical transducing layer 128 can be transferred to the optical waveguide 118, thus modulating light traveling to through the optical waveguide 118. The modulated signal may travel along the same optical waveguide 118 or other optical waveguide to a signal generator / detector 130 (FIG.1) at which the signal can be demodulated and the corresponding perturbation determined. This can prevent the need for a multiplexing circuit at the bottom of the well. The stress induced in the optical waveguide 118 may be proportional to the electromotive force. Variations in the electromotive force over time can be determined. By following these variations, it can be determined whether the electromagnetic properties, such as the resistivity, of the subsurface formation 104 have changed, e.g., due to the substitution of the fluid in the reservoir. The interrogation of the optical waveguide 118 at different lengths coated with the electro-optical transducing layer 128 may allow the optical waveguide 118 to function as a network of sensors for measuring the electromotive force at different points along the the length of the optical fiber cable 116.

The electro-optical transducing layer 128 may comprise any suitable material for inducing stress at the optical waveguide 118 in response to the electromagnetic field. Examples of such materials may include, but are not limited to, piezoelectric materials and electrorestrictive materials. Suitable combinations of materials may also be used. Specific examples of such materials may include lead titanate-zirconate (PZT), lead and magnesium niobate, lead and nickel niobate, lead and manganese niobate, antimony and lead stannate , zinc and lead niobate, lead titanate, lead and magnesium tantalate, lead and nickel tantalate, doped lead titanate, lead and magnesium niobate (PT: PMN), and combinations of these. The foregoing piezoelectric / electrostrictive materials may also comprise an additive of the oxide or other type of compound of, for example, lanthanum, barium, niobium, zinc, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium, tantalum, tungsten, nickel, manganese, lithium, strontium and bismuth. The electro-optical transducing layer 128 may also be a composite which comprises a piezoelectric / electrostrictive material and a polymer. For example, the piezoelectric / electrostrictive material may be dispersed in a polymer matrix. Examples of suitable polymers may include, but are not limited to, polyvinylidene fluoride (PVDF). The composite of the electro-optical transducing layer 128 comprises a composite of the piezoelectric / electrorestrictive material and the polymer can provide the functions of the electro-optical transducer layer 128 and the polymer pad 120 and thus it can be used in the polymer buffer place 120 .

Some electrorestrictive materials, eg, PT: PMN) may have relatively low Curie temperatures, e.g., 150 ° C, which could limit their use in high temperature wells, such as wells. deep water. However, notwithstanding these temperature limits for some materials, well monitoring system 100 can still be used in offshore and onshore wells. For example, target tank temperatures for coal bed methane in some areas (eg, Black Warrior Basin in western Alabama) can typically range from 27 to 57 ° C. But also, the optical waveguide 118 with the electro-optical transducing layer 128 can also be used on the sea floor, where the temperature can be low, e.g., 0 to 30 ° C, or at the of the surface 110 where the temperature can be between 0 and 60 ° C.

Any suitable technique may be used to coat the electro-optical transducing layer 128 on the optical waveguide 118. The homogeneity of the bond between the optical waveguide 118 and the electron transduction layer Optical 128 can ensure that the electrostriction is accurately transferred to the stress of the fiber. Any difference in temperature and gravity stress between the electro-optical transducing layer 128 and the optical waveguide 118 can result in uniform stresses, fractures, and even breaks. In order to limit such damages, the electro-optical transduction layer 128 may have partial or total cuts to release the voltage during deployment. This may be particularly applicable for gravity-induced stress in systems deployed by freely suspended work cable. The electro-optical transducing layer 128 may have a thickness, e.g., from about 15 microns to about 60 microns.

[0025] Referring again to FIG. 1, the optical fiber cable 116 may be coupled to a signal generator / detector 130 at the surface 110 which may generate a signal to be transmitted to the bottom of the well. As an example, the optical fiber cable 116 may terminate at a surface interface with an optical port adapted for the one or more coupling fibers (e.g., optical waveguides 118) in the fiber cable. The light source may transmit light pulses along the optical fiber cable 116. The constraint induced along one or more waveguides Optical waves 118 in the optical fiber cable 116 through the electro-optical transducing layer 128 can modify the light pulses to provide measurements, e.g., of the electromotive force. These changes may affect the amplitude, phase, and frequency content of the light pulses, allowing the detectors to produce, in response, an electrical output signal indicative of receiver measurements. Some systems may use multiple fibers, in which case an additional light source and detector may be used for each fiber, or the existing source and detector may be periodically switched between the fibers. The signal generator / detector 130 may use interrogation techniques to extract and demodulate the constraint imposed at different locations along the optical waveguide 118 for determining the electromotive force at different locations along the the length of the optical waveguide 118. In this way, e.g., the resistivity can be mapped along the optical fiber cable 116.

The signal generator / detector 130 may be coupled to a computer system 132 which may be coupled to a signal generator / detector through a control line 134. The computer system 132 may comprise a central processing unit 136, a screen 138 and a capture device 140 (eg, keyboard, mouse, etc.) as well as a computer medium 142 (eg, optical disks, magnetic disks) which can store a representative code aforementioned methods. The computer system 132 may be adapted to receive signals from the signal generator / detector 130 representative of the electromotive force measurements. The computer system 132 may act as a data acquisition system and possibly as a data processing system that analyzes the measurements of the electromotive force, eg, to obtain subterranean parameters and to monitor them during the course of time. time. The electromotive force measurements received at the computer system 132 can be interpreted in terms of a resistivity model of the subterranean formation 104. The resistivity model can, in turn, be interpreted in terms of fluid in the pores of the the formation, allowing the monitoring of reservoir fluids over time, allowing the determination of fluid substitution during water injection and dewatering.

Referring now to Figures 3-5, several examples of an optical waveguide 118 at least partially coated with an electro-optical transduction layer 128 are illustrated. In each of these examples, at least one length of the optical guide 118 is covered with the electro-optical transduction layer 128. As illustrated, the optical waveguide 118 can form an optical loop and be coupled to a generator / signal detector 130 for interrogation. Any suitable interrogation technique of the optical waveguide 118 for distributed stress measurements may be used, including interrogation techniques that utilize interferometric methods such as Mach-Zehnder, Michelson. Sagnac, Cabry-Perot, etc. Even if the interrogation techniques are not described in detail here. a measured phase shift may represent a measure of the stress induced and. thus, a measure of the electromotive force. The optical waveguide 118 may be deployed within a cable enclosed in the casing, such as the optical fiber cable 116 of FIG.

In the example of FIG. 3, a length of the optical waveguide 118 may be covered by the electro-optical transduction layer 128 from point 142 to point 144, through which the optical waveguide 118 of point 146 to point 148 does not include an electro-optic transduction coating. The length of the optical waveguide 118 covered with the electro-optical transducing layer 128 may range from 10 m to 10,000 m, moreover, about 10 m or more, about 50 m, about 100 m, about 500 m or more, about 1000 m or more.

In the example of FIG. 4, the optical waveguide 118 may comprise a plurality of electro-optical transduction layers 128 spaced along the optical waveguide 118. The remainder of the optical waveguide 118 may not include an electro-optic transduction coating. Optical waveguide 118 may need only periodic coating since parts of optical waveguide 118 may be placed in one or more formations that are not of interest. Any suitable technique used to prepare an optical waveguide 118 with spaced apart electro-optic transduction layers 128, including splicing of the covered and uncoated optical waveguides, toward each other for forming the optical waveguide 118. The length of the spaced electro-optical transduction layers 128 may range from 1m to 1000m with a spacing of from 1m to 1000m. For example, the electro-optic transduction layers 128 may be about 1 m in length with a spacing of about 2 m. As another example, the electro-optic transduction layers 128 may be about 10 m in length with a spacing of about 1 m. The length and spacing of the electro-optical transducing layers 128 may be selected to provide a desired sensitivity for electromotive force detection. The optical waveguide 118 may also be covered only periodically by the electro-optical transducing layers 128 to avoid predictable stress patterns on the optical waveguide 118.

In the example of Figure 5, the optical waveguide 118 may be periodically covered with a material 148 which does not demonstrate electrostriction. Examples of materials 148 may include, without limitation, a standard fiber sheath. As illustrated, the material 148 may be spaced along the optical waveguide 118. Therefore, when the optical waveguide 118 is covered by electro-optic transduction layers 128, the electro-optical transduction layers 128 optical 128 only periodically binds to the optical waveguide 118, e.g., when the material 148 is absent. The length and spacing of the material 148 may be selected, e.g., based on a desired sensitivity with respect to the detection of the electromotive force.

As previously described, the electro-optical transduction layer (s) 128 on the optical waveguide 118 may be used in the measurement of the electromotive force. The electromotive force (V), measured in volts, can be defined as the linear integral of the electromagnetic field E along a path I between points a and b along the direction of the waveguide axis optical:

0) in which the vectors E and dl are collinear. The convention for an integral linear quantity such as the electromotive force is a positive reference at the beginning of the integration path.

Since the electro-optical transduction layer (s) 128 may be exposed to a time-varying electromagnetic field, e.g., with a component in the direction of the optical waveguide axis 118, the optical transduction layer (s) 128 may deform and thus produce a corresponding constraint in the optical waveguide.

The electro-optical transduction layer (s) 128 may comprise an electro-restrictive material, such as a piezoelectric ceramic, in which the stress in the optical waveguide 118 may be linearly proportional to the electromotive force:

(2) wherein k represents the electro-restrictive response parameter for the electrooptic transduction layer (s) 128.

The electro-optical transduction layer (s) 128 may comprise an electro-restrictive material, such as an electrorestrictive ceramic, in which the stress in the optical waveguide 118 may be linearly proportional to the square of the electromotive force. :

(3) wherein k represents the electro-restrictive response parameter for the electro-optical transduction layer (s) 128.

The optical fiber can be excited by an external electromagnetic field of low harmonic frequency over time, which induces a stress along the direction of the axis of the optical waveguide. By remotely measuring the stress along the direction of the axis of the optical waveguide, and knowing the functional relationship between the stress and the low frequency and harmonic electromotive force over time VncosQt, whether by the equations (2) or (3), the electromotive force can be detected.

A high frequency carrier voltage V0) coset may be applied through the electro-optical transduction layer (s) 128 while the electromotive force VncosQt i at low frequency is detected. The non-linear electrorestrictive response may cause signal mixing so that low frequency signals at Ω can be converted into stresses at ω ± Ω sideband frequencies. This may be an advantage, allowing the electromotive force to be detected at higher frequencies at which low frequency electromagnetic noise (e.g. from telluric currents) may not be dominant, resulting in a signal on noise. improved.

Referring now to Figure 6, another exemplary arrangement of an optical waveguide 118 at least partially covered with electro-optical transduction 128 is illustrated. In the example of FIG. 6, the optical waveguide 118 may be wound around the casing 106 or other downhole equipment, such as a production tube, a tool body, a cable line, etc. In general, the systems and methods disclosed herein may have a sensitivity along the direction of the optical waveguide 118. However, by winding the optical waveguide 118 around the casing 106, as shown in FIG. , an azimuth sensitivity can be obtained. As will be understood, the optical waveguide 118 may be deployed within a cable enclosed within the casing, such as the fiber optic cable 116 shown in FIG. 2, for example.

FIG. 7 illustrates another example of a well monitoring system 100 which may be representative of a well which is monitored using an optical fiber cable 116, which may contain a guide for optical wave 118 at least partially covered by one or more electro-optical transduction layers 128, as shown in FIGS. 2-5, for example. In the example of Figure 7, a series of valves 150 may be used to cap the well. A casing 106 may be placed in the wellbore 102. A production tube or a cabled line 152 may be inserted into the casing 106. The optical fiber cable 116 may be coupled within the casing 106, either by attachment at an inner portion of the casing 106 or a production tube or a cable line 152. In addition, the optical fiber cable 116 may be placed in or coupled to an inner portion of the casing 106. The optical fiber cable 116 may comprise one or more optical waveguides 118 (eg Figures 2-5) function as a sensor array for measuring the electromotive force at different points along the length of the optical fiber cable 116. Specific information regarding the fluids in the subterranean formation 104 may be inferred from the signal analysis from the optical fiber cable 116. The signal generator / detector 130 may be coupled to the signal cable. optical fiber 116 for receiving signals from the optical fiber cable 116.

FIG. 8 illustrates an example of a well monitoring system 100 which may be representative of a subsea well which must be monitored using an optical fiber cable 116, which may contain a optical waveguide 118 at least partially covered by one or more electro-optical transduction layers 128, as shown in FIGS. 2-5, for example. In the example of FIG. 8, a semi-submersible platform 154 can be placed above the seafloor 156. An underwater conduit 158 can extend from a bridge 160 of the semi-submersible platform 154 to an installation Well below the wellhead installation 162, the wellbore 102 can penetrate the subterranean formation 104. Cement 108 may surround the tubing 106 in the wellbore 102. The well may be adapted to guide a desired fluid (eg, oil, gas, etc.) from the wellbore bottom 102 to the earth's surface. Perforations 164 may be made in the wellbore 102 to facilitate the flow of fluid 166 from the subterranean formation 104 to the wellbore 102 and then to the surface.

As illustrated, the optical fiber cable 116 may be placed along an outer portion of the casing 106 or along the wellbore 102. Furthermore, the optical fiber cable 116 may be placed in, or coupled to an inner portion of casing 106. Optical fiber cable 116 may include one or more optical waveguides 118 (e.g., Figures 2-5) function as a sensor array for measuring electromotive force. at different points along the length of the optical fiber cable 116. Specific information regarding the fluids contained in the subterranean formation 104 may be inferred from the analysis of the signal from the optical fiber cable 116. The generator / detector signal 130 may be coupled to the optical fiber cable 116 for receiving signals from the optical fiber cable 116.

FIG. 9 illustrates an example of a well monitoring system 100 that may be representative of an underwater well which must be monitored using an optical fiber cable 116, which may contain a optical waveguide 118 at least partially covered by one or more electro-optical transduction layers 128, as shown in FIGS. 2-5, for example. In the example of FIG. 8, the optical waveguide 118 may be placed on a surface, such as the seafloor 156. The optical fiber cable 116 may comprise one or more optical waveguides 118 (e.g. FIGS. 2-5) function as a network of sensors for measuring the electromotive force at different points along the length of the optical fiber cable 116. Specific information regarding the fluids contained in the underground formation 104 can be be derived from the signal analysis from the optical fiber cable 116. The signal generator / detector 130 may be coupled to the optical fiber cable 116 for receiving signals from the optical fiber cable 116.

FIG. 10 illustrates an example of a well monitoring system 100 that may be representative of a well that must be monitored using an optical fiber cable 116, which may contain a guide for optical wave 118 at least partially covered by one or more electro-optical transduction layers 128, as shown in FIGS. 2-5, for example. In the example of Figure 10, a casing 106 may be placed in the wellbore 102. The optical fiber cable 116 may be placed along an outer portion of the casing 106. In addition, the fiber optic cable The optical fiber cable 116 may comprise one or more optical waveguides 118 (e.g., FIGS. for measuring the electromotive force at different points along the length of the optical fiber cable 116. Specific information regarding the fluids contained in the underground formation 104 can be deduced from the analysis of the signal from the optical fiber cable 116. The signal generator / detector 130 may be coupled to the optical fiber cable 116 for receiving signals from the optical fiber cable 116.

As illustrated, a hoist 168 may be used to deploy a wired tool 170 in the wellbore 102. The wired tool 170 may include a transmitter 172, e.g., which can generate an electromagnetic signal, in which wherein the electromagnetic signal can be detected by the optical fiber cable 116. The waveform of the transmitting current can be solved from the measured electromotive force to recover the response of the electromotive pulse. From a plurality of different wired tool positions 170 in the wellbore 102, this electromotive pulse response can be used for the calibration of the electromotive force measurements. On the other hand, the wired tool 170 may be used to determine the position of the optical fiber cable 116, particularly the optical waveguide 118 at least partially covered by the electro-optical transduction layer (s) 128 (e.g. Figures 2-5), in the wellbore 102. In order to determine the azimuth position, the optical fiber cable 116 can be excited with an electrical source and the acoustic signal obtained can be measured with an acoustic sensor. For example, the wired tool 170 can pass through the wellbore 102 generating an electromagnetic field from the transmitter 172, e.g., with an electrode in contact with the casing 106. The induced stress must generate an acoustic signal that can be detected with an acoustic transducer 174, e.g., on a wired tool 170. The direction can be obtained by having multiple acoustic transducers 174 placed azimuth around a wired tool body 170. This can be particularly advantageous for locating the optical fiber cable 116, e.g., prior to certain operations of the wellbore 102, such as perforation.

For the purposes of illustration, the examples of Figures 1 and 7-10 illustrate a wellbore 102 which is oriented vertically. However, the methods and systems described herein can be used in other wellbore configurations 102, including a horizontal penetration configuration or an oblique wellbore configuration. In addition, the examples of Figures 1 and 6-10, illustrate various arrangements in which the optical waveguide 118 disclosed herein can be used in well monitoring. It should be understood that the present disclosure should not be limited to any given technique for placement of an optical waveguide 118 in a well, but is intended to cover the use of the optical waveguide 118 in the well monitoring, whether placed in casing 106, outside casing 106, at a surface (e.g., seafloor 156), etc.

The disclosed examples of the electromotive force detection may be simultaneously deployed with other optical fiber-based detection systems, including, without limitation, acoustic array, temperature and stress detection. As an example, an optical waveguide 118 at least partially covered by one or more electro-optical transduction layers 128, as disclosed herein, may be deployed from the same cable enclosed in the casing, such as cable of optical fiber 116 of FIG. 2, in the form of one or more additional detection systems based on the optical fiber. Deployment of fiber-based systems in the same casing-enclosed cable can provide operational stability, eg in high pressure environments (eg, 35,000 psi) while being chemically reactive and continuous vibrations for a prolonged period of time, conditions that could be encountered on the seafloor or in oilfield wells. The optical waveguides 118 may be multimodal so that a plurality of detection network methods may be interrogated simultaneously.

In some examples, the temperature-dependent characteristics of the electro-optical transduction layer (s) 128 may be characterized for the calibration of the measurements of the electromotive force. In practice, the temperature or temperature gradient across the interrogation intervals of the electromotive force detection system can be measured and interrogated remotely from a temperature sensing network system.

In the additional examples, the measurements of the electromotive force can be corrected to take account of the effects of the vibration by using an acoustic detection network system, such as the well monitoring system 100 of FIGS. 1 and 7. 10. The cancellation of the acoustic and vibration noise can be performed through the length of the optical waveguide 118 which is not sensitized (eg, the length or lengths without electro-optical transduction layer (s) 128) as long as they are deployed close to each other. This can be achieved if fiber-based systems are deployed in the same cable enclosed by the casing.

As described herein, the acoustic detection system network (e.g., the well monitoring system 100 of Figs. 1 and 7-10) may not consume sensor energy. This can be particularly advantageous for deployment in underwater environments, in which the energy available from a submarine nodule can be very limited. In some cases, the disclosed optical waveguides 118 may be fabricated to enable efficient mass production and ease of deployment. For example, for permanent electromagnetic reservoir monitoring, the optical waveguides 118 may be prefabricated and transported on a cable drum for ease of deployment.

[0049] There may be several potential benefits to the systems and methods disclosed herein, and only a few can be mentioned here. One of the many potential benefits of processes and systems may be that the electromotive force detection network of an electromagnetic field can be used for monitoring the reservoir. Another advantage lies in the fact that the electrodes would not be necessary for measuring the electromotive force (or the electromagnetic field). Another advantage is that the connection of the independent electromagnetic sensors with the optical waveguide would not be necessary, thus simplifying the manufacture and deployment of the system, eg in permanent tank monitoring systems.

[0050] To facilitate a better understanding of the present claims, the following 5 examples of certain aspects of the description are given. The following examples should in no way limit or define the overall scope of the claims.

EXAMPLES

[0051] In recent years, there has been a significant investment in coal bed methane deposits for unconventional gas production in some regions, such as Australia and the United States. In a tank of coal bed methane, the metal can be stored in coal-litter or dissolved in fossil water. The primary mechanism for the production of wet methanol can be through the Darcy flow through the drying or depressurization of the coal seams over several months. During dewatering, the metal is desorbed from the coal and as the permeability of the formation increases, it flows more easily to the wellbore.

Figure 11 illustrates a hypothetical model showing the production of coal bed methane and resistivity over time. As shown in FIG. 11, the production of methane may be negligible during the initial stages of desiccation. However, over time, water production may decrease and methane production may increase. I Gradually, the coal can be desiccated and degassed. This is generally not accelerated since rapid dewatering can result in shrinkage of the reservoir and thus reduced permeability due to pressure overload. The production can be increased by the injection of carbon dioxide, since the carbon dioxide absorbs preferentially on the coal; forcing the desorption of methane and its diffusion in the lime system.

From a rock physics perspective, it can be assumed that dewatering is a substitution of fluid; and therefore, the resistivity must change. The resistivity of a "wet coal" can be less than 100 ohm-m (depending on the resistivity of fossil water), while the resistivity of "dry coal" can often be greater than 500 ohm-m (eg ., 1000+ ohm-m). Therefore, electrical resistance tomography can be used to monitor the gasification of underground coal.

Figure 12 illustrates a hypothetical ground model of a tank of coal bed methane subjected to degassing. As illustrated, the initial resistivity of the tank may be 50 ohm-m and the final resistivity of the tank may be 500 ohm-m. The electromagnetic tank monitoring system may include a power source 112, which may be an unipolar electric transmitter with a current of 1A, and an electromotive force sensing network system, both of which are deployed in the same well. . As illustrated, the electromotive force detection network system may comprise an optical waveguide 118 having a length of 20 feet covered with an electro-optical transducing layer 118, the optical waveguide 118 can be interrogated over a length of 20 feet. The system can operate at 1 Hz. Figure 13 illustrates the electromotive force signal for the 20-foot length of the optical waveguide 118 as it would be measured for the model of Figure 12. The signal level is The order of V. FIG. 14 illustrates the sensitivity that would be measured over a 20-foot length of the optical waveguide 118 for the model of FIG. 12.

The foregoing description describes several embodiments of the systems and methods of use described herein, which may contain different process steps and other combinations of components. It should be understood that, although individual embodiments can be presented here, the present disclosure covers all combinations of the described embodiments, including, without limitation, the various combinations of components, process step combinations and the properties of the system. It will be understood that the compositions and methods are described in terms of "comprising", "containing" or "including" various components or steps, the compositions and methods may also "consist essentially of" or "consist of" various components and steps. In addition, the indefinite articles "a" or "an" as used in the claims are defined herein to mean one or more of the element they introduce.

For the sake of brevity, only certain intervals are explicitly described here. However, intervals from any lower limit may be combined with any upper limit to cover an interval not explicitly indicated, and intervals from any lower limit may be combined with any other lower limit to cover a non-explicitly indicated range of similarly, intervals from any upper limit may be combined with any other upper limit to indicate an interval not explicitly stated. In addition, whenever a numerical range with a lower bound and an upper bound is specified, any inclusive number or range within the range is specifically included. In particular, each range of values (of the form, "from about a to about b" or, equivalently, "from about a to b", or, equivalently, "from about ab") indicated here should be understood as describing each number and interval within the widest range of values if it is not explicitly stated. Thus, each individual point or value may serve its own lower or upper limit combined with any other point or individual value or other lower or upper limit to indicate an interval not explicitly stated.

Therefore, the present embodiments are well adapted to achieve the objectives and advantages mentioned and also those that are inherent in the present invention. The particular embodiments described above are illustrative only, since the present invention may be modified and practiced in different but equivalent ways which will be apparent to those skilled in the art who benefit from the teachings of the invention. Although only individual embodiments are described, the invention covers any combination of all embodiments. In addition, no limitation is provided to the construction or design details described herein, other than those described in the claims below. In addition, the terms in the claims have their clear and ordinary meaning, except in the case of explicit and clear indication other defined by the applicant. It is therefore obvious that the particular illustrative embodiments described above may be altered or modified, and all such variations are considered to be within the scope and spirit of these embodiments. In the event of a conflict in the use of a word or term in this description and in at least one patent or other document that may be referred to herein, the definitions that are consistent with that description must be adopted.

Claims (22)

Claims What is claimed: A well monitoring system comprising: a power supply that generates an electromagnetic field in an underground formation; and a network of electromotive force sensors for measuring the electromotive force at one or more points along a length of the electromotive force sensor array, the electromotive force sensor array including a guide of the electromotive force an optical wave and an electro-optical transducing layer which overlaps one or more lengths of the optical waveguide. The system of claim 1, wherein the electromotive force sensor array is installed in a wellbore. The system of claim 1, wherein the electromotive force sensor array is installed on an ocean floor. The system of claim 1, wherein the optical waveguide is wrapped around the casing installed in a wellbore. The system of claim 1, wherein the electromotive force sensor array is placed in an interior of a casing installed in a wellbore. The system of claim 1, wherein the electromotive force sensor array is coupled to an exterior of a surface of a casing installed in a wellbore. The system of claim 1, wherein the electromotive force sensor array can be placed in an optical fiber cable that includes an optical waveguide bundle. The system of claim 1, wherein the electrooptic transducing layer may comprise a material selected from the group consisting of a piezoelectric material, an electrostrictive material, and a combination thereof. The system of claim 1, wherein the electrooptic transduction layer comprises an electro-optical transducing material and a polymer. The system of claim 1, wherein the length of the optical waveguide coated with the electro-optical transducing layer is from 1m to 10,000m. The system of claim 1, wherein the optical waveguide is periodically covered with the electro-optical transducing layer to provide spaced apart electro-optical transducing layers which, each individually, has a length ranging from 1 m to 1000 m and a spacing ranging from 1 m to 1000 m. The system of claim 11, wherein the optical waveguide is covered with a material between the spaced electro-optical transduction layers, wherein the material does not bind to the electrooptic transducing layer. The system of claim 11, further comprising a computer system for monitoring the measured electromotive force. A well monitoring method comprising: generating an electromagnetic field in a subterranean formation; and measuring the electromotive force at one or more points along an array of electromotive force sensors, the electromotive force sensor array comprising an optical waveguide and an electro transduction layer -optical covering one or more lengths of the optical waveguide The method of claim 14, wherein the electromotive force sensor array is installed in a wellbore. The method of claim 14, wherein the electromotive force sensor array is installed on an ocean floor. ' The method of claim 14, wherein the electromotive force sensor array is wrapped around a casing installed in a wellbore. The method of claim 14, wherein the measurement of the electromotive force comprises inducing a stress in the optical waveguide in response to the electromagnetic field. The method of claim 14, further comprising generating an electromagnetic signal with a wired tool lowered into the wellbore; detecting the electromagnetic signal with the electromotive force sensor array; and determining the response of the electromotive pulse of the electromotive force sensor array at one or more positions of the wired tool. The method of claim 14, further comprising generating an electromagnetic field with a wired tool lowered into the wellbore to energize the optical waveguide; and measuring an acoustic signal generated by the optical waveguide in response to the electromagnetic field using acoustic transducers placed on the wired tool. The method of claim 14, further comprising monitoring the measured electromotive force to determine the fluid substitution time intervals in the subterranean formation. The method of claim 14, further comprising monitoring the measured electromotive force to determine the drying of a coal bed methane tank.